This invention relates to dynamoelectric machines employing superconducting field windings, and more particularly to a support system for mounting the rotor torque tube and superconducting winding within the rotor in cantilever fashion from the one end of the rotor shaft.
In a generator having a field winding, the superconducting field winding is supported within a torque tube located concentrically with the rotor shafts. The superconducting winding is connected to a source of electric current and a source of coolant through means located within the hollow rotor shaft. In prior art dynamoelectric machine designs employing superconducting field windings, the torque tube is mounted to the rotor shaft by torque tube extensions at each end thereof. The mounting of each end requires that some means be supplied to accommodate thermal contraction due to the cooling of the rotor field winding to cryogenic temperatures, usually by liquid helium, to a temperature of about 4.degree. Kelvin. Further, the torque tube extensions form thermal conduction paths which must be cooled in order to limit the amount of heat added to the coolant, which can cause transition of the coolant, usually helium, from the liquid state to the gaseous state. Such a mounting structure for a superconducting rotor torque tube is illustrated in U.S. Pat. No. 4,082,967, issued Apr. 4, 1978 to Laskaris, and assigned to the instant assignee. Thermal distance extensions are attached to each end of the torque tube and separately cooled.
A mounting structure is shown in U.S. Pat. No. 4,117,357, issued Sept. 26, 1978 to Baumann, which incorporates a flexible coupling 48 at the driven end 6 of the rotor to mount the torque tube within the rotor shaft. As described in Baumann, each of the ends of the torque tubes exhibit a temperature gradient along their axial lengths which rises from the temperature of liquid helium, approximately 4.degree. Kelvin, at the superconducting winding to room temperature at the flanges 23 and 24. Each end of the torque tube must be mounted and cooled to accommodate axial thermal expansion and contraction and also to accommodate the mechanical stresses experienced by the rotor elements during a short circuit.
A cryogenic current lead construction is described and illustrated in my prior U.S. Pat. No. 4,091,298, issued May 23, 1978 and assigned to the instant assignee, which incorporates the use of vaporized coolant to cool the current leads and the torque tube extension used to attach the torque tube at the end of the rotor shaft.
A support structure for the cryogenic temperature portion of a rotor shaft is described in U.S. Pat. No. 4,060,742, issued Nov. 29, 1977 to Litz. The mounting structure uses a torque tube extension 19 at one end of the cryogenic portion, and a plurality of spokes at the opposite end of the cryogenic portion to mount the cryogenic portion of the rotor within the torque tube. Litz describes a balancing between the stiffness of the support spokes and heat loss as the controlling design criteria for his structure.
To accommodate thermal expansion and contraction, the support for the cryogenic field winding and the torque tube must be so designed that unacceptable stress will not be applied to the torque tube or superconducting winding or the rotor shaft during either transition from room temperature to cryogenic temperature or from cryogenic temperature to room temperature. Further, the support structure must be able to withstand the angular deflection imposed upon the torque tube support during short circuit faults in the system. The support structure must also be designed to minimize the heat leak to the cryogenic temperature region in order to minimize the quantity of liquid helium vaporized during operation of the machine. Furthermore, the support structure should be such that the machine rotor can be easily assembled and tested.
Accordingly, it is an object of my invention to provide a torque tube and field winding support structure which will accommodate axial thermal expansion and contraction, and provide the required stiffness to resist angular deflection at fault current condition.
Another object of the instant invention is to provide the necessary support for the rotor torque tube and field winding while presenting a minimum of conduction paths for heat leak to the cryogenic section of the rotor and without requiring a complicated mechanical structure.